Earth's internal heat budget

Earth's internal heat budget is about heat that comes from the Earth itself, not heat from the Sun. 

The flow of heat from Earth's interior to the surface is estimated at 47±2 terawatts (TW).Davies J.H. & D.R. 2010. Earth's surface heat flux. Solid Earth, 1(1), 5–24p. It comes from two main sources in roughly equal amounts. There is the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust. Secondly, there is the primordial heat left over from the formation of Earth.Donald L. Turcotte & Gerald Schubert 2002. Geodynamics. Cambridge University Press. ISBN 978-0-521-66624-4

As many people know, the deeper down you go, the hotter the Earth gets. Mine shafts are a good example of this.

 Radiogenic heat 

This is still being produced. but its amount reduces very slowly as time passes. Remember, these radioactive elements are produced in supernovae, and are quite different from the Sun, which is mostly hydrogen. The planets are completely different from the Sun, historically and in their make-up.

 Primordial heat 
Primordial heat is the heat lost by the Earth as it continues to cool from its original formation, in contrast to its still actively-produced radiogenic heat. 

The Earth core's heat flow—heat leaving the core and flowing into the overlying mantle is thought to be due to primordial heat. It is estimated as 5–15 TW.Lay T; Hernlund J., & Buffett, B.A. 2008. Core–mantle boundary heat flow. Nature Geoscience, 1(1), 25–32. 

 References 

Dalrymple G. Brent 2004. Ancient Earth, ancient skies: the age of Earth and its cosmic surroundings. Stanford University Press. ISBN 0-8047-2331-1

Category:Earth
Category:Heat transfer